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Campbell Biology: Concepts & Connections

Tenth Edition

Chapter 3

The Molecules of Cells

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Introduction

Most adults cannot properly digest dairy products.

These people are lactose intolerant, because they lack the enzyme lactase.

This illustrates the importance of biological molecules, such as lactase, in the daily functions of living organisms.

Figure 3.0_1

Figure 3.0_1 What does evolution have to do with drinking milk?

Figure 3.0_2

Figure 3.0_2 Chapter 3: Big Ideas

Long Description:

The details of the figure are as follows:

Introduction to organic compounds: An image shows ball-and-stick model with a central black sphere bonded to 4 small, white spheres in tetrahedral shape.

Carbohydrates: An image shows a colony of bees in a honey comb.

Lipids: An image shows bilipid layer of a membrane with oval heads on the outer side and two tails for each head on the inner side.

Proteins: An image shows the three-dimensional structure of a protein.

Nucleic acids: An image shows the double helical structure of a D N A molecule.

Introduction to Organic Compounds

3.1 Life’s Molecular Diversity Is Based on the Properties of Carbon (1 of 2)

Carbon’s ability to bond with four other atoms is the basis for building large and diverse organic compounds.

Carbon chains form the backbone of most organic molecules.

Isomers have the same molecular formula but different structures.

Hydrocarbons are composed of only carbon and hydrogen.

Student Misconceptions and Concerns

Students might need to be reminded about the levels of biological organization. Without such a review, the relationship between atoms, monomers, and polymers can be confusing as each is discussed. Consider noting these relationships somewhere in the classroom (such as on the board) where students can quickly glance for reassurance. (3.1)

General biology students might not have previously taken a chemistry course. The concept of molecular building blocks that cannot be seen can be abstract and difficult to comprehend for such students. Concrete examples from our diets and good images will increase comprehension. (3.1–3.3)

Teaching Tips

One of the great advantages of carbon is its ability to form up to four bonds, permitting the assembly of diverse components and branching configurations. Challenge your students to find another element that might also permit this sort of adaptability. (Like carbon, silicon has four electrons in its outer shell.) (3.1)

Toothpicks and gumdrops (or any other pliable small candy) permit the quick construction of chemical models. Different candy colors can represent certain atoms. The model of the methane molecule in Figure 3.1 can thus easily be demonstrated (and consumed)! (3.1)

3.1 Life’s Molecular Diversity Is Based on the Properties of Carbon (2 of 2)

Checkpoint question Methamphetamine occurs as two isomers: one is the addictive illegal drug known as “crank”; the other is a sinus medication. How can you explain these differing effects?

Checkpoint Question Response

Isomers have different structures, or shapes, and the shape of a molecule usually determines the way it functions in the body.

Student Misconceptions and Concerns

Teaching Tips

Figure 3.1a

Figure 3.1a A model of methane and the tetrahedral shape of a molecule

Figure 3.1b

Figure 3.1b Four ways in which carbon skeletons can vary

Long Description:

Characteristics of Skeleton

Definition

Examples

Length

carbon skeletons vary in length

ethane is two single bonded carbons surrounded by hydrogens, propane is three single bonded carbons surrounded by hydrogens

Double bonds

carbon skeletons may have double bonds, which can vary in location

1 butene which has a 4 carbon middle with the double bond between the first and second carbon, 2 butene which has a 4 carbon middle with the double bond between the second and third carbon

Branching

carbon skeletons may be unbranched or branched

butane is unbranched, isobutane is branched with a carbon coming off the center, second carbon

Rings

carbon skeletons may be arranged in rings. In the abbreviated ring structures, each corner represents a carbon and its attached hydrogens.

cyclohexane is six carbons single bonded in a ring with two hydrogens off of each carbon, benzene is a six carbon ring with every other bond a double bond and one hydrogen off of each hydrogen

Figure 3.1b_1

Figure 3.1b_1 Four ways in which carbon skeletons can vary (part 1: length)

Figure 3.1b_2

Figure 3.1b_2 Four ways in which carbon skeletons can vary (part 2: double bonds)

Figure 3.1b_3

Figure 3.1b_3 Four ways in which carbon skeletons can vary (part 3: branching)

Figure 3.1b_4

Figure 3.1b_4 Four ways in which carbon skeletons can vary (part 4: rings)

Animation: Isomers 2

Animation: Carbon Skeletons

Animation: Isomers

3.2 A Few Chemical Groups are Key to the Functioning of Biological Molecules (1 of 2)

An organic compound’s properties depend on the

size and shape of its carbon backbone and

atoms attached to that skeleton.

Hydrophilic functional groups give organic molecules specific chemical properties.

Table 3.2 illustrates six important chemical groups.

Student Misconceptions and Concerns

Teaching Tips

A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions to different structures. (3.2)

Table 3.2 Important Chemical Groups Of Organic Compounds (1 of 3)

Checkpoint question Identify the chemical groups that do not contain carbon.

Checkpoint Question Response

The hydroxyl, amino, and phosphate groups

Long Description:

The table is as follows.

Chemical group

Example

A hydroxyl, or O H, group shown as single bond O H.

A carbon skeleton of alcohol shows two carbons single bonded to each other. The left carbon is bonded to three hydrogen molecules. The right carbon is bonded to two hydrogen molecules and a hydroxyl, or O H group.

A carbonyl, two single bonds connect to a carbon double bonded to an oxygen, group.

• A carbon skeleton of three carbons. The first carbon is single bonded to the second carbon and the second is single bonded to the third carbon. The middle carbon is a carbonyl group. The first and third carbons are single bonded to three hydrogens.

• Three carbons are single bonded together. The first two carbons are bonded to three hydrogens and two hydrogens respectively. The third carbon is double bonded to an oxygen as a carbonyl group, and single bonded to a hydrogen.

A carboxyl. or C O O H group.

A carboxylic acid. Two carbons are single bonded to each other. The left carbon is single bonded to three hydrogens, and the right carbon is double bonded to an oxygen and single bonded to an O H group. The carboxylic acid yields the following in a reversible reaction. An ionized form of carboxylic acid which is a single bonded C double bonded to an O with a O H also single bonded to the C. The O H of the carboxyl group loses the positive hydrogen atom becoming negative.

An amino group which is single bonded N H 2.

An amine. A carbon is single bonded to a nitrogen. The carbon is also single bonded to three hydrogens. The nitrogen is single bonded to two hydrogens. Beside the amine is an additional H positive ion. The amine reacts with a hydrogen ion to produce its ionized form in a reversible reaction. The ionized form is the amine where the nitrogen now has a positive charge and is bonded to three hydrogens.

A phosphate group, has a single bond O P O 3 with a charge of negative 2.

An organic phosphate, A T P. Adenosine, is single bonded to a chain of alternating oxygen and phosphorus atoms. Each phosphorus is also double bonded to an oxygen and single bonded to a negative oxygen. The last phosphorus in the chain is double bonded to an oxygen, and single bonded to two negatively charged oxygens.

A methyl C H 3 group with a single bond at one end.

A methylated compound shows a ring of four carbons and two nitrogens. The carbon on the top right is the first carbon and the carbons are numbered one to four in a clockwise direction. Carbon one and two are double bonded to each other, carbon two is single bonded to nitrogen, the nitrogen is single bonded to carbon three, carbon three is single bonded to a second nitrogen, the nitrogen is double bonded to the fourth carbon. The first carbon has a methyl group attached to it, the second carbon is single bonded to a hydrogen, the first nitrogen is single bonded to a hydrogen, the third carbon is double bonded to an oxygen, and the fourth carbon is bonded to amino group.

3.2 A Few Chemical Groups Are Key to the Functioning of Biological Molecules (2 of 2)

The sex hormones testosterone and estradiol (a type of estrogen) differ only in the groups of atoms highlighted in Figure 3.2.

Student Misconceptions and Concerns

Teaching Tips

A drill with interchangeable drill bits is a nice analogy to carbon skeletons with different functional groups. The analogy relates the role of different functions to different structures. (3.2)

Figure 3.2

Figure 3.2 Differences in the chemical groups of sex hormones

Long Description:

Estradiol has a hydroxyl group where testosterone has a carbonyl group, and doesn’t have a group where testosterone has a methane group.

Figure 3.2_1

Figure 3.2_1 Differences in the chemical groups of sex hormones (part 1)

Figure 3.2_2

Figure 3.2_2 Differences in the chemical groups of sex hormones (part 2)

3.3 Cells Make Large Molecules from a Limited Set of Small Molecules (1 of 2)

The four classes of biological molecules contain very large molecules.

They are often called macromolecules because of their large size.

They are also called polymers because they are made from identical or similar building blocks strung together.

The building blocks of polymers are called monomers.

Student Misconceptions and Concerns

Teaching Tips

Train cars linking together to form a train is a nice analogy to linking monomers to form polymers. Consider noting that as the train cars are joined, a puff of steam appears—a reference to water production and a dehydration reaction when linking molecular monomers. (3.3)

The authors note that the great diversity of polymers mainly results from variable arrangements of monomers, with different sequences possible from combinations or permutations of the same monomers. Consider illustrating this by simply asking students how many different ways we can arrange the letters A, B, and C, using each letter, and only once, to form three-lettered words. The answer is six permutations: ABC, ACB, BAC, BCA, CBA, CAB (the factorial of 3). And if letters can be repeated, the answer is 27 (= 33): AAA, BBB, CCC, ABB, ACC, etc. (3.3)

3.3 Cells Make Large Molecules from a Limited Set of Small Molecules (2 of 2)

Monomers are linked together to form polymers through dehydration reactions.

Polymers are broken apart by hydrolysis.

These reactions are mediated by enzymes, specialized macromolecules that speed up reactions.

Checkpoint question Suppose you eat some cheese. What reactions must occur for the protein of the cheese to be broken down into its amino acid monomers and then for these monomers to be converted to proteins in your body?

Checkpoint Question Response

During digestion, proteins are broken down into amino acids by hydrolysis. New proteins are formed in your body cells from these monomers by dehydration reactions.

Student Misconceptions and Concerns

Teaching Tips

Figure 3.3

Figure 3.3 Dehydration reaction building a polymer (left); hydrolysis breaking down a polymer (right)

Long Description:

The first illustration shows a dehydration reaction. Monomers are depicted by purple circles. In the dehydration reaction, a polymer is built and a new bond is formed. Polymers and monomers are flanked by a hydrogen and a hydroxyl group. A short polymer made up of three monomers reacts with an unlinked monomer. The hydroxyl group of the short polymer reacts with the hydrogen of the unlinked monomer. This releases a water molecule and creates a longer polymer made up of 4 monomers. The second illustration shows a hydrolysis reaction. In a hydrolysis reaction, a polymer is made into smaller parts and a bond is broken. A polymer made up of 4 monomers is flanked by a hydrogen and a hydroxyl group. A water molecule comes in and helps to break the bond between the third and fourth carbons, and the polymer breaks up into a polymer made up of three monomers and an unlinked monomer.

Figure 3.3_1_1

Figure 3.3_1_1 Dehydration reaction building a polymer (part 1, step 1)

Long Description:

In this illustration, monomers are depicted by purple circles. Polymers and monomers are flanked by a hydrogen and a hydroxyl group. A short polymer made up of three monomers reacts with an unlinked monomer. The hydroxyl group of the short polymer reacts with the hydrogen of the unlinked monomer.

Figure 3.3_1_2

Figure 3.3_1_2 Dehydration reaction building a polymer (part 1, step 2)

Long Description:

In this illustration, monomers are depicted by purple circles. In the dehydration reaction, a polymer is built and a new bond is formed. Polymers and monomers are flanked by a hydrogen and a hydroxyl group. A short polymer made up of three monomers reacts with an unlinked monomer. The hydroxyl group of the short polymer reacts with the hydrogen of the unlinked monomer. This releases a water molecule and creates a longer polymer made up of 4 monomers.

Figure 3.3_2_1

Figure 3.3_2_1 Hydrolysis breaking down a polymer (part 2, step 1)

Figure 3.3_2_2

Figure 3.3_2_2 Hydrolysis breaking down a polymer (part 2, step 2)

Long Description:

In this illustration, monomers are depicted by purple circles. Polymers and monomers are flanked by a hydrogen and a hydroxyl group. In a hydrolysis reaction, a polymer is made into smaller parts and a bond is broken. A polymer made up of 4 monomers is flanked by a hydrogen and a hydroxyl group. A water molecule comes in and helps to break the bond between the third and fourth carbons, and the polymer breaks up into a polymer made up of three monomers and an unlinked monomer.

Animation: Polymers

Carbohydrates

3.4 Monosaccharides are the Simplest Carbohydrates

Carbohydrates range from small sugar molecules (monomers) to large polysaccharides.

Sugar monomers are monosaccharides.

A monosaccharide generally has a formula that is a multiple of C H 2 O and contains hydroxyl groups and a carbonyl group.

Checkpoint question Write the formula for a monosaccharide that has three carbons.

Checkpoint Question Response

C3H6O3

Student Misconceptions and Concerns

The abstract nature of chemistry can be discouraging to many students. Consider starting out this section of class by examining the chemical groups on a food nutrition label. Candy bars with peanuts are particularly useful because they contain significant amounts of all three sources of calories (carbohydrates, proteins, and lipids). (3.4)

Consider reinforcing the three main sources of calories with food items that clearly represent each group. Bring clear examples to class as visual references. For example, use a can of Coke or a bag of sugar (or cotton candy) for carbohydrates, a tub of margarine for lipids, and some beef jerky for protein (although some fat and carbohydrates might also be included). (3.4–3.7)

Teaching Tips

If your lectures will eventually include details of glycolysis and aerobic respiration, this is a good point to introduce the basic concepts of glucose as fuel. Just introducing this conceptual formula might help: consuming glucose and breathing oxygen produce water and usable energy (that can be used to build ATP) plus heat and carbon dioxide exhaled in our breath. (3.4)

Active Lecture Tips

See the Activity “Reviewing Macromolecules” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. (3.4–3.7)

Figure 3.4a

Figure 3.4a Bees with honey, a mixture of two monosaccharides

Figure 3.4b

Figure 3.4b Structures of glucose and fructose

Long Description:

The glucose skeleton is made up of a vertical chain of six carbons labeled 1 through 6 from top to bottom. Carbon one is part of a carbonyl group. It is double bonded to an oxygen and single bonded to a hydrogen. Carbons two, four, and five are single bonded to a hydroxide group on the right and a hydrogen on the left. Carbon three is single bonded to a hydrogen on the right and a hydroxide group on the left. Carbon five is single bonded to a hydroxide on the right, a hydrogen on the left, and another hydrogen. The fructose skeleton is made up of a vertical chain of six carbons as well. The skeleton is identical to that of glucose from carbons 3 through 6. The only changes are carbon one is single bonded to a hydroxyl to the right and an additional hydrogen and carbon two is a carbonyl carbon.

Figure 3.4c

Figure 3.4c Three representations of the ring form of glucose

Long Description:

In the first ring, the structural formula is given. There is a hexagon of carbons and an oxygen. The top right vertex of the hexagon is the oxygen, and carbons one through five are found on the hexagon moving clockwise.

● Carbon one is bonded to a hydrogen and a hydroxyl group. The hydroxyl group is below the hydrogen group.

● Carbon two is bonded to a hydrogen and a hydroxyl group. The hydroxyl group is down and the hydrogen is up.

● Carbon three is bonded to a hydrogen and a hydroxyl group. The hydroxyl group is up and the hydrogen is down.

● Carbon four is bonded to a hydrogen and a hydroxyl group. The hydroxyl group is below the hydrogen group.

● Carbon five is bonded to carbon six found in C H 2 O H.

In the second ring, an abbreviated structure is shown. The hexagon is the same, but the carbons in the ring are not shown. In the third ring, a simplified structure is shown. The only element shown in the structure is the oxygen on the top right vertex of the hexagon.

3.5 Two Monosaccharides Are Linked to Form a Disaccharide

Two monosaccharides (monomers) can bond to form a disaccharide in a dehydration reaction.

Checkpoint question Lactose, as you read in the chapter introduction, is the disaccharide sugar in milk. It is formed from glucose and galactose. The formula for both these monosaccharides is C 6 H 12 O 6. What is the formula for lactose?

Checkpoint Question Response

C12H22O11

Student Misconceptions and Concerns

Teaching Tips

Learning the definitions of word roots is invaluable when learning science. Learning the meaning of the prefix word roots “mono” (one), “di” (two), and “poly” (many) helps to distinguish the structures of various carbohydrates. (3.5)

Active Lecture Tips

Figure 3.5_1

Figure 3.5_1 Disaccharide formation by a dehydration reaction (step 1)

Figure 3.5_2

Figure 3.5_2 Disaccharide formation by a dehydration reaction (step 2)

Long Description:

The two monosaccharides are both glucose. The O H group of carbon one from one glucose molecule and the hydrogen from the OH group of carbon four from the other glucose react to release a water molecule and make a disaccharide, maltose.

Animation: Disaccharides

3.6 Connection: Are We Eating Too Much Sugar?

The F D A recommends that only 10% of daily calories come from added sugar.

Research supports the correlation between high sugar intake and adverse health effects.

Checkpoint question Sugars are often described as “empty calories.” What do you think that means from a nutrition standpoint?

Checkpoint Question Response

Added sugars provide energy but they do not provide other nutrients, such as protein, fats, vitamins, or minerals.

Student Misconceptions and Concerns

Teaching Tips

The extent of sugar consumption can be surprising to students. Consider asking each student to identify a product that they have consumed that has added sugar. (3.6)

Consider an assignment for students to find reliable sources that discuss high rates of sugar consumption in the modern diet. The key, of course, is in the quality of the resource. Consider limiting their search to established nonprofit organizations (American Cancer Society, American Heart Association, etc.) and peer-reviewed journals. (3.6)

Active Lecture Tips

See the Activity “What Ingredients Make Up Your Snack Food” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. (3.6)

Figure 3.6

Figure 3.6 The amount of sugar an average U.S. adult eats in a year compared to recommendations from the World Health Organization (WHO) and the Food and Drug Administration (FDA)

Long Description:

The graph has the row headings W H O, F D A, and average American. The graph reads as the table below indicates.

Yearly Consumption, shown with 5 pound bags of sugar

4 bags, 20 pounds

8 bags, 40 pounds

26 bags, 130 pounds

3.7 Polysaccharides Are Long Chains of Sugar Units

Starch and glycogen are storage polysaccharides.

Cellulose is structural, found in plant cell walls.

Chitin is a component of insect and crustacean and fungal cell walls.

Checkpoint question Compare and contrast starch and cellulose, two plant polysaccharides.

Checkpoint Question Response

Both are polymers of glucose, but the bonds between glucose monomers have different shapes. Starch functions mainly for sugar storage. Cellulose is a structural polysaccharide that is the main material of plant cell walls.

Student Misconceptions and Concerns

Teaching Tips

A simple exercise demonstrates the enzymatic breakdown of starches into sugars. If students place an unsalted cracker in their mouths, holding it in their mouths while it mixes well with saliva, they might soon notice that a sweeter taste begins to emerge. The salivary enzyme amylase begins the digestion of starches into disaccharides, which may be degraded further by other enzymes. These disaccharides are the source of the sweet taste. (3.7)

The text notes that cellulose is the most abundant organic molecule on Earth. Ask your students why this is true. (3.7)

The cellophane wrap often used to package foods is a biodegradable material derived from cellulose. Consider challenging students to create a list of other cellulose-derived products (such as paper). (3.7)

An adult human may store about half a kilogram of glycogen in the liver and muscles of the body, depending on recent dietary habits. A person who begins dieting might soon notice a weight loss of 2–4 pounds (1–2 kilograms) over several days, reflecting reductions in stored glycogen, water, and intestinal contents (among other factors). (3.7)

Active Lecture Tips

Figure 3.7

Figure 3.7 Polysaccharides of plants and animals

Long Description:

All examples of polysaccharides are made up of glucose monomers.

Polysaccharide

Found in

Made up of

Starch

potato tuber cell

long chains of glucose molecules

Glycogen

muscle tissue

long chains of glucose molecules, more branched than starch.

Cellulose

plant cell wall

parallel chains of cellulose molecules are joined by hydrogen bonds. the bonds between the glucose molecules are different than the ones in starch and glycogen, they alternate rather than being all on one side

Figure 3.7_1

Figure 3.7_1 Polysaccharides of plants and animals (part 1: starch)

Figure 3.7_2

Figure 3.7_2 Polysaccharides of plants and animals (part 2: glycogen)

Figure 3.7_3

Figure 3.7_3 Polysaccharides of plants and animals (part 3: cellulose)

Long Description:

The chemical structure of cellulose consists of parallel chains of cellulose molecules that are joined by hydrogen bonds. The bonds between the glucose molecules are different than the ones in starch and glycogen; they alternate rather than being all on one side

Figure 3.7_4

Figure 3.7_4 Polysaccharides of plants and animals (part 4: photo)

Animation: Polysaccharides

Lipids

3.8 Fats Are Lipids That Are Mostly Energy-Storage Molecules (1 of 2)

Lipids are diverse hydrophobic (water-fearing) compounds composed largely of carbon and hydrogen.

Fats (triglycerides) consist of glycerol linked to three fatty acids.

Some fatty acids contain one or more double bonds, forming unsaturated fatty acids. Unsaturated fatty acids are typical of plant oils.

Fats with the maximum number of hydrogens are called saturated fatty acids. Saturated fatty acids are found in animal fats.

Student Misconceptions and Concerns

Students may struggle with the concept that a pound of fat contains more than twice the calories of a pound of sugar. It might seem that a pound of food would potentially add on a pound of weight. Other students may have never understood the concept of calories in the diet, simply following general guidelines of avoiding fatty foods. Furthermore, fiber and water have no caloric value but add to the weight of food. Consider class discussions that explore student misconceptions about calories, body weight, and healthy diets. (3.8)

Students might struggle to extrapolate the properties of lipids to their roles in an organism. Ducks float because their feathers repel water instead of attracting it. Hair on our heads remains flexible because of oils produced in our scalp. Examples such as these help connect the abstract properties of lipids to concrete examples in our world. (3.8–3.11)

Teaching Tips

The text in Module 3.8 notes the common observation that vinegar and oil do not mix. A simple demonstration can help make this point. In front of the class, mix together colored water and a yellow oil (corn or canola oil works well). Shake up the mixture and then watch as the two separate. (You may have a mixture already made ahead of time that remains separated; however, the dye may bleed between the oil and the water.) Placing the mixture on a well-illuminated imaging device makes for a dramatic display of hydrophobic activity! (3.8)

The text notes that a gram of fat stores more than twice the energy of a gram of polysaccharide, such as starch. You might elaborate with a simple calculation to demonstrate how a person’s body weight would vary if the energy stored in body fat were stored in carbohydrates instead. If a 100-kg man carried 25% body fat, he would have 25 kg of fat in his body. Fat stores about 2.25 times more energy per gram than carbohydrate. What would be the weight of the man if he stored the fat energy in the form of carbohydrate? (2.25  25 = 56.25 kg of carbohydrate + 75 kg (nonfat body weight) = 131.25 kg, an increase of 31.25%.) (3.8)

Active Lecture Tips

See the Activity “Drawing Hydrophobic and Hydrophilic Interactions” on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. (3.8, 3.10)

3.8 Fats Are Lipids That Are Mostly Energy-Storage Molecules (2 of 2)

Hydrogenated vegetable oils are unsaturated fats that have been converted to saturated fats by adding hydrogen.

This hydrogenation creates trans fats, which are associated with health risks.

Checkpoint question Explain why fats are hydrophobic.

Checkpoint Question Response

The three fatty acid tails of a fat molecule contain only nonpolar C—H bonds, which do not mix well with polar water molecules.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Figure 3.8a

Figure 3.8a A dehydration reaction that will link a fatty acid to glycerol

Long Description:

The fatty acid is a chain of sixteen carbons. The carbon at the end of the chain is part of a carboxyl group. The glycerol is made up of a chain of three carbons and each carbon is bonded to a hydroxyl group. The O H from the carboxyl group of the fatty acid reacts with the hydrogen from the hydroxyl group of the glycerol to release a water molecule and link the fatty acid and the glycerol.

Figure 3.8b

Figure 3.8b A fat molecule (triglyceride) consisting of three fatty acids linked to glycerol

Long Description:

Two of the fatty acids are chains of sixteen carbons where the carbon at the end of the chain is a carbonyl group. The third fatty acid is a chain of sixteen carbons where the end is a carbonyl group and carbons eight and nine share a double bond.

Figure 3.8c

Figure 3.8c Types of fats

Figure 3.8c_1

Figure 3.8c_1 Types of fats (part 1: saturated fats)

Figure 3.8c_2

Figure 3.8c_2 Types of fats (part 2: unsaturated fats)

Animation: Fats

3.9 Scientific Thinking: Scientific Studies Document the Health Risks of Trans Fats (1 of 2)

By the 1990s, partially hydrogenated oils were common in countless foods.

Recent research has shown that trans fats pose an even greater health risk than saturated fats.

The scientific studies establishing the risks of trans fats were of two types.

In experimental controlled feeding trials, diets contained different proportions of saturated, unsaturated, and partially hydrogenated fats.

Many other scientific studies on dietary health effects are observational.

Student Misconceptions and Concerns

Teaching Tips

Margarine in stores commonly comes in liquid spray or squeeze containers, in tubs, and in sticks. These forms reflect increasing amounts of hydrogenation, gradually increasing the stiffness from a liquid, to a firmer spread, to a firm stick of margarine. As noted in the text, recent studies have suggested that unsaturated oils become increasingly unhealthy as they are hydrogenated. Students might therefore remember that as margarine products increase in stiffness, they generally become less healthy. Public attention to hydrogenation and the health risks of the resulting trans fats are causing changes in the use of products containing trans fats. (3.9)

Active Lecture Tips

3.9 Scientific Thinking: Scientific Studies Document the Health Risks of Trans Fats (2 of 2)

Checkpoint question What is the difference between a retrospective and a prospective study?

Checkpoint Question Response

A retrospective study “looks backward” to assess risk factors or benefits that correlate with current health status. A prospective study follows a group forward, monitoring certain factors and recording health outcomes over a period of time.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Figure 3.9

Figure 3.9 Relative risk of heart disease associated with increased intake of specific types of fats

Long Description:

The data is represented by the following table.

Relative Risk

Change in risk

Type of fat

2.00

100% increase in risk

blank

1.93

between 50 and 100%

Trans fat

1.50

50% increase in risk

blank

1.17

between 0 and 50%

Saturated fat

1.00

Baseline, no risk difference

blank

0.81

Under 0%

Monounsaturated fat

0.62

Under 0%

Polyunsaturated fat

0.50

50% decrease in risk

blank

0.25

75% decrease in risk

blank

3.10 Phospholipids and Steroids Are Important Lipids with a Variety of Functions

Phospholipids are components of cell membranes.

Steroids include cholesterol and some hormones.

Cholesterol is a common component in animal cell membranes and is also the precursor for making other steroids, including sex hormones.

Checkpoint question Compare the structure of a phospholipid with that of a fat.

Checkpoint Question Response

The three fatty acid tails of a fat molecule contain only nonpolar C—H bonds, which do not mix well with polar water molecules.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Figure 3.10a

Figure 3.10a Chemical structure of a phospholipid molecule

Long Description:

The figure shows that a phospholipid is made up of a glycerol and two fatty acids. One of the fatty acids is a chain of sixteen carbons, where the carbon at the end of the chain is a carbonyl group. The second fatty acid is a chain of sixteen carbons where the end is a carbonyl group and carbons eight and nine share a double bond. The glycerol is made up of a three carbon chain where the last carbon is attached to a phosphate group. The head of the phospholipid is made up of the glycerol and phosphate group and is hydrophilic. The tails of the phospholipid are made up of the two fatty acid chains and are hydrophobic. The phospholipids are shown as gray ovals that represent the heads, and yellow arms that represent the tails

Figure 3.10b

Figure 3.10b Section of a phospholipid membrane

Long Description:

The figure shows a section of the membrane to depict how the phospholipids interact. The phospholipids group by their heads into a sheet, and two sheets interact by their tails so that the hydrophobic tails are not exposed to water and the hydrophilic heads are

Figure 3.10c

Figure 3.10c Cholesterol, a steroid

3.11 Connection: Anabolic Steroids Pose Health Risks

Anabolic steroids are synthetic variants of the male hormone testosterone that are abused by some athletes with serious consequences.

Checkpoint question Explain why fats and steroids, which are structurally very different, are both classed as lipids.

Checkpoint Question Response

The three fatty acid tails of a fat molecule contain only nonpolar C—H bonds, which do not mix well with polar water molecules.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Figure 3.11

Figure 3.11 Bodybuilder

Proteins

3.12 Proteins Have a Wide Range of Functions and Structures (1 of 2)

Proteins are involved in nearly every dynamic function in your body and are very diverse.

Proteins function as

enzymes,

transport proteins embedded in cell membranes,

defensive proteins, such as antibodies,

signal proteins such as many hormones,

receptor proteins,

contractile proteins found within muscle cells,

structural proteins such as collagen, and

storage proteins.

Student Misconceptions and Concerns

The functional significance of protein shape is an abstract molecular example of form and function relationships, which might be new to some students. The binding of an enzyme to its substrate is a type of molecular handshake, which permits specific interactions. To help students think about form and function relationships, share some concrete analogies in their lives—perhaps flathead and Phillips screwdrivers that match the proper type of screws or the fit of a hand into a glove. (3.12)

Teaching Tips

Most cooking results in changes in the texture and color of food. The brown color of a cooked steak is the product of the denaturation of proteins. Fixatives such as formalin also denature proteins and cause color changes. Students who have dissected vertebrates will realize that the brown color of the muscles makes it look as if the animal has been cooked. (3.12)

Active Lecture Tips

3.12 Proteins Have a Wide Range of Functions and Structures (2 of 2)

Proteins are composed of differing arrangements of a common set of just 20 amino acid monomers.

The functions of different types of proteins depend on their individual shapes.

In the process of denaturation, a protein unravels, loses its specific shape, and loses its function.

Checkpoint question Why does a denatured protein no longer function normally?

Checkpoint Question Response

The function of each protein is a consequence of its specific shape, which is lost when a protein denatures.

Student Misconceptions and Concerns

Teaching Tips

Active Lecture Tips

Figure 3.12a

Figure 3.12a Ribbon model of the protein lysozyme

Figure 3.12b

Figure 3.12b Space-filling model of the protein lysozyme

Figure 3.12c

Figure 3.12c Fibrous silk proteins of a spider’s web.

3.13 Proteins Are Made from Amino Acids Linked by Peptide Bonds (1 of 2)

Protein diversity is based on different sequences of amino acids, monomers that contain

an amino group,

a carboxyl group,

an H atom, and

an R group, all attached to a central carbon.

The R groups distinguish 20 amino acids, each with specific properties.

Teaching Tips

Many analogies help students appreciate the diversity of proteins that can be made from just 20 amino acids. The authors note that our language uses combinations of 26 letters to form words. Proteins are much longer “words,” creating even more diversity. Another analogy is to trains. This builds upon the earlier analogy suggested when polymers were introduced. Imagine making different trains about 100 cars long, using any combination of 20 types of railroad cars. Mathematically, the number of possible trains is 20100, a number beyond imagination. (3.13)

The difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! (3.13, 3.14)

Active Lecture Tips

3.13 Proteins Are Made from Amino Acids Linked by Peptide Bonds (2 of 2)

Amino acid monomers are linked together in a dehydration reaction,

joining the carboxyl group of one amino acid to the amino group of the next amino acid, and

creating a peptide bond.

Additional amino acids can be added by the same process to create a chain of amino acids called a polypeptide.

Checkpoint question By what process do you digest the proteins you eat into their individual amino acids?

Checkpoint Question Response

By hydrolysis, adding a molecule of water back to break each peptide bond

Teaching Tips

The difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! (3.13, 3.14)

Active Lecture Tips

Figure 3.13a

Figure 3.13a General structure of an amino acid

Figure 3.13b

Figure 3.13b Examples of amino acids with hydrophobic and hydrophilic R groups

Long Description:

A table of example R groups of amino acids.

Hydrophobic

Hydrophilic

Leucine, has a r group of two carbon backbone with two C H 3 groups at the end

Serine has an r group of a C H 2 linked to O H, Aspartic acid has an r group with a two carbon backbone with a negatively charge O attached and a double bonded O attached

Figure 3.13c_1

Figure 3.13c_1 Peptide bond formation (step 1)

Figure 3.13c_2

Figure 3.13c_2 Peptide bond formation (step 2)

Long Description:

The carboxyl group of one amino acid reacts with the amino group of another amino acid. This releases water and forms a bond between the carboxylic carbon and nitrogen called a peptide bond.

3.14 Visualizing the Concept: A Protein’s Functional Shape Results from Four Levels of Structure (1 of 2)

A protein can have four levels of structure:

A protein’s primary structure is the sequence of amino acids in its polypeptide chain.

Its secondary structure is the coiling or folding of the chain, stabilized by hydrogen bonds.

The tertiary structure is the overall three-dimensional shape of a polypeptide, resulting from interactions among R groups.

Proteins made of more than one polypeptide have quaternary structure.

Teaching Tips

The difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! (3.13, 3.14)

An examination of the fabrics and weave of a sweater might help students understand the levels of protein structure. Although not a perfect analogy, levels of organization can be better appreciated. Teasing apart a single thread reveals a simpler organization of smaller fibers woven together. In turn, threads are interlaced into a connected fabric, which may be further twisted and organized into a pattern or structural component of a sleeve. Challenge students to identify the limits of this analogy and identify aspects of protein structure not included (such as the primary structure of a protein, its sequence of amino acids). (3.14)

Active Lecture Tips

3.14 Visualizing the Concept: A Protein’s Functional Shape Results from Four Levels of Structure (2 of 2)

Checkpoint question If a genetic mutation changes the primary structure of a protein, how might this destroy the protein’s function?

Checkpoint Question Response

Primary structure determines the secondary and tertiary structure due to the chemical nature of the R groups of the amino acids in the chain. Even a slight change may affect a protein’s shape and thus its function.

Teaching Tips

The difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! (3.13, 3.14)

Active Lecture Tips

Figure 3.14_0_1

Figure 3.14_0_1 A protein’s functional shape results from four levels of structure (step 1)

Long Description:

The details of the diagram are as follows:

In primary structure, the amino acids are bonded in a chain with an amino end and a carboxyl end. Each amino acid in the chain are represented by three letter abbreviations. Each specific amino acid has an R group. The repeated sequence of single bond N single bond C single bond C single bond, with attached single bond H and double bond O, but not the R groups, is called the polypeptide backbone. An example shows polypeptide bonds that connect the 127 amino acids of a transthyretin polypeptide and part of the chain is shown.

Figure 3.14_0_2

Figure 3.14_0_2 A protein’s functional shape results from four levels of structure (step 2)

Long Description:

The details of the primary and secondary structures are as follows:

Type of Structure

Description

Primary

The amino acids are bonded in a chain with an amino end and a carboxyl end. Each amino acid in the chain are represented by three letter abbreviations. Each specific amino acid has an R group. The repeated sequence of single bond N single bond C single bond C single bond, with attached single bond H and double bond O, but not the R groups, is called the polypeptide backbone. An example shows polypeptide bonds that connect the 127 amino acids of a transthyretin polypeptide and part of the chain is shown.

Secondary

Secondary structures are maintained by hydrogen bonds between atoms of the polypeptide backbone, shown as dotted lines. There are two types of secondary structures. Alpha helix and beta pleated sheet. In the beta pleated sheets, the carboxyl end is pointed to by a flat arrow.

Figure 3.14_0_3

Figure 3.14_0_3 A protein’s functional shape results from four levels of structure (step 3)

Long Description:

The details of the primary, secondary, and tertiary structures are as follows:

Type of Structure

Description

Primary

Secondary

Tertiary

A tertiary structure is stabilized by interactions between R groups, such as the clustering of hydrophobic R groups in the center of the molecule, and hydrogen bonds, ionic bonds, and disulfide bridges between hydrophilic R groups. An example of a transthyretin polypeptide has one alpha helix region and several beta pleated sheets, which are compacted into a globular shape.

Figure 3.14_0_4

Figure 3.14_0_4 A protein’s functional shape results from four levels of structure (step 4)

Long Description:

The details of the primary, secondary, tertiary, and quaternary structures are as follows:

Type of Structure

Description

Primary

Secondary

Tertiary

Quaternary

The four identical polypeptides, or subunits, of transthyretin are precisely associated into a functional protein. Interactions similar to those involved in tertiary structures hold these subunits together.

Figure 3.14

Figure 3.14 A protein’s functional shape results from four levels of structure

Long Description:

A series of diagrams explain four different structures of proteins.

Type of Structure

Description

Primary

Secondary

Secondary structures are maintained by hydrogen bonds between atoms of the polypeptide backbone, shown as dotted lines. There are two types of secondary structures. alpha helix and beta pleated sheet. In the beta pleated sheets, the carboxyl end is pointed to by a flat arrow.

Tertiary

Quaternary

Figure 3.14_1

Figure 3.14_1 A protein’s functional shape results from four levels of structure (part 1: primary structure)

Long Description:

The details of the diagram are as follows:

Figure 3.14_2

Figure 3.14_2 A protein’s functional shape results from four levels of structure (part 2: secondary structures)

Long Description:

The details of the diagram are as follows:

Figure 3.14_3

Figure 3.14_3 A protein’s functional shape results from four levels of structure (part 3: tertiary structure)

Long Description:

The details of the diagram are as follows: A tertiary structure is stabilized by interactions between R groups, such as the clustering of hydrophobic R groups in the center of the molecule, and hydrogen bonds, ionic bonds, and disulfide bridges between hydrophilic R groups. An example of a transthyretin polypeptide has one alpha helix region and several beta pleated sheets, which are compacted into a globular shape.

Figure 3.14_4

Figure 3.14_4 A protein’s functional shape results from four levels of structure (part 4: quaternary structure)

Long Description:

The details of the diagram are as follows:

Animation: Protein Structure Introduction

Animation: Primary Protein Structure

Animation: Secondary Protein Structure

Animation: Tertiary Protein Structure

Animation: Quaternary Protein Structure

Nucleic Acids

3.15 The Nucleic Acids D N A and R N A Are Information-Rich Polymers of Nucleotides (1 of 2)

The monomers that make up nucleic acids are nucleotides.

Nucleotides are composed of a sugar, a phosphate group, and a nitrogenous base.

D N A is a double helix.

R N A is a single polynucleotide chain.

D N A and R N A serve as the blueprints for proteins and thus control the life of a cell.

D N A is the molecule of inheritance.

Student Misconceptions and Concerns

Module 3.15 is the first time the authors present the concept of transcription and translation, discussed extensively in later chapters. The basic conceptual flow of information from DNA to RNA to proteins is essential to these later discussions. A flow chart that also relates the location where these processes occur in a eukaryotic cell will help to cement this fundamental transmission of genetic information. (3.15)

Teaching Tips

The “NA” in the acronyms DNA and RNA stands for “nucleic acid.” Students often do not make this association without assistance. (3.15)

When discussing the sequence of nucleotides in DNA and RNA, consider challenging your students with the following questions based on prior analogies. If the 20 possible amino acids in a polypeptide represent “words” in a long polypeptide sentence, how many words are possible in the language of a DNA molecule? (Answer: Four nucleotides, GCAT, are possible). Are these the same “words” used in RNA? (Answer: No. Uracil substitutes for thymine.) (3.15)

Active Lecture Tips

Figure 3.15a

Figure 3.15a A nucleotide

Long Description:

The oxygen of the phosphate group is bonded to the methyl group on the fourth carbon of the deoxyribose cyclopentene ring. The nitrogenous base’s nitrogen is bonded to the first carbon of the deoxyribose cyclopentene ring.

Figure 3.15b

Figure 3.15b A polynucleotide

Figure 3.15c

Figure 3.15c DNA double helix

Figure 3.15d_1

Figure 3.15d_1 The flow of genetic information in the building of a protein (step 1)

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Figure 3.15d_2

Figure 3.15d_2 The flow of genetic information in the building of a protein (step 2)

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Figure 3.15d_3

Figure 3.15d_3 The flow of genetic information in the building of a protein (step 3)

Long Description:

A gene is transcribed from D N A into R N A. The R N A. is then translated into a protein that is made up of a chain of amino acids. The gene a section of D N A which is shown at the top with a blue, ribbon like double helix. The transcription occurs to change the D N A into R N A which is shown as a single pink wavy line. And the protein which is a chain of amino acids is shown at the bottom as a series on connected spheres.

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3.15 The Nucleic Acids D N A and R N A Are Information-Rich Polymers of Nucleotides (2 of 2)

Checkpoint question What roles do complementary base pairing play in the functioning of D N A?

Checkpoint Question Response

Complementary base pairing makes possible the precise replication of DNA, ensuring that genetic information is faithfully transmitted every time a cell divides. It also ensures that RNA molecules carry accurate instructions from DNA for the synthesis of proteins.

Student Misconceptions and Concerns

Teaching Tips

The “NA” in the acronyms DNA and RNA stands for “nucleic acid.” Students often do not make this association without assistance. (3.15)

Active Lecture Tips

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3.16 Evolution Connection: Lactose Tolerance Is a Recent Event in Human Evolution

Different mutations in D N A have led to lactose tolerance in several human groups whose ancestors raised dairy cattle.

Researchers identified three new mutations in 43 ethnic groups in East Africa that keep the lactase gene permanently turned on.

Checkpoint question Explain how lactose tolerance involves three of the four major classes of biological macromolecules.

Checkpoint Question Response

By hydrolysis, adding a molecule of water back to break each peptide bond

Teaching Tips

The difference between a polypeptide and a protein is analogous to the relationship between a long strand of yarn and a sweater knitted from yarn. Proteins are clearly more complex! (3.13, 3.14)

Active Lecture Tips

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Figure 3.16

Figure 3.16 Lactose tolerance: two different cultures, two different mutations—same adaptations

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Figure 3.16_1

Figure 3.16_1 Lactose tolerance: two different cultures, two different mutations—same adaptations (part 1)

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Figure 3.16_2

Figure 3.16_2 Lactose tolerance: two different cultures, two different mutations—same adaptations (part 2)

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You Should Now Be Able to (1 of 2)

Describe the importance of carbon to life’s molecular diversity.

Describe the chemical groups that are important to life.

Explain how a cell can make a variety of large molecules from a small set of molecules.

Define monosaccharides, disaccharides, and polysaccharides and explain their functions.

Define lipids, phospholipids, and steroids and explain their functions.

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You Should Now Be Able to (2 of 2)

Explain how trans fats are formed in food. Describe the evidence that suggests that eating trans fats is more unhealthy than consuming saturated fats.

Describe the chemical structure of proteins and the importance of proteins to cells.

Describe the chemical structure of nucleic acids and explain how they relate to inheritance.

Explain how lactose tolerance has evolved in humans.

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Figure 3.10

Figure 3.10 Detail of a phospholipid molecule

Long Description:

A phospholipid is made up of a glycerol and two fatty acids. One of the fatty acids is a chain of sixteen carbons, where the carbon at the end of the chain is a carbonyl group. The second fatty acid is a chain of sixteen carbons where the end is a carbonyl group and carbons eight and nine share a double bond. The glycerol is made up of a three carbon chain where the last carbon is attached to a phosphate group. The head of the phospholipid is made up of the glycerol and phosphate group and is hydrophilic. The tails of the phospholipid are made up of the two fatty acid chains and are hydrophobic. The phospholipids are shown as gray ovals that represent the heads, and yellow arms that represent the tails. The section of the membrane shows how the phospholipids interact. The phospholipids group by their heads into a sheet, and two sheets interact by their tails so that the hydrophobic tails are not exposed to water and the hydrophilic heads are.

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Table 3.2 Important Chemical Groups of Organic Compounds (2 of 3)

Table 3.2_1 Important chemical groups of organic compounds (part 1)

Long Description:

The details of the table are as follows.

Chemical group

Example

A hydroxyl, or O H, group shown as single bond O H.

A carbonyl, two single bonds connect to a carbon double bonded to an oxygen, group.

A carboxyl, or C O O H group.

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Table 3.2 Important Chemical Groups of Organic Compounds (3 of 3)

Table 3.2_2 Important chemical groups of organic compounds (part 2)

Long Description:

The details of the table are as follows:

Chemical group

Example

An amino group which is single bonded N H 2.

A phosphate group, has a single bond O P O 3 with a charge of negative 2.

A methyl C H 3 group with a single bond at one end.

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Figure 3.UN01

Figure 3.UN01 Reviewing the concepts, 3.3

Long Description:

In the dehydration reaction, the short polymer is made up of a chain of at least two amino acids. The monomer is made up of one amino acid, flanked by two hydrogen atoms. One of the hydrogen atoms of the monomer and the hydroxyl group of the short polymer react to form a longer polymer and release a water molecule. In the hydrolysis reaction, which is just the reverse of the dehydration reaction, the longer polymer is made up of three amino acid flanked by hydrogen. The polymer reacts with a water molecule and breaks down into a monomer and a short polymer. The monomer is made up of one amino acid flanked by two hydrogen atoms. The short polymer is made up of a chain of at least two amino acids.

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Figure 3.U N02

Figure 3.UN02 Connecting the concepts, question 1

Long Description:

A table of important molecule types has 4 rows and 3 columns.

Classes of Molecules and Their Components

Functions

Examples

Carbohydrates

A monosaccharide is made up of a carbon hexagon.

Energy for cell, raw material, blank b, plant cell support

blank a, starch, glycogen, blank c

Lipids. don’t form polymers

The components of a fat molecule, a rectangular glycerol and long fatty acid tail.

Energy storage, blank e, hormones

blank d, phospholipids, blank f

Proteins

An amino acid with blanks g, h, and i for the three components of the amino acid. The amino acid is a center c connected to an H and three structures.

blank j, blank k, blank l, transport communication, blank n, storage, receive signals

lactase, hair, tendons, muscle proteins, blank m, signal proteins, antibodies, proteins in seeds, receptor protein

Nucleic Acids

A nucleotide with blanks o, p, and q for the three components of the nucleotide.

heredity, blank s

blank r, D N A and R N A

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Figure 3.U N02_1

Figure 3.UN02_1 Connecting the concepts, question 1 (part 1)

Long Description:

The details of the table are as follows:

Classes of Molecules and Their Components

Functions

Examples

Carbohydrates

A monosaccharide is made up of a carbon hexagon.

Energy for cell, raw material, blank b, plant cell support

blank a, starch, glycogen, blank c

Lipids. don’t form polymers

The components of a fat molecule, a rectangular glycerol and long fatty acid tail.

Energy storage, blank e, hormones

blank d, phospholipids, blank f

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Figure 3.U N02_2

Figure 3.UN02_2 Connecting the concepts, question 1 (part 2)

Long Description:

The details of the table are as follows:

Classes of Molecules and Their Components

Functions

Examples

Proteins

An amino acid with blanks g, h, and i for the three components of the amino acid. The amino acid is a center c connected to an H and three structures.

blank j, blank k, blank l, transport communication, blank n, storage, receive signals

lactase, hair, tendons, muscle proteins, blank m, signal proteins, antibodies, proteins in seeds, receptor protein

Nucleic Acids

A nucleotide with blanks o, p, and q for the three components of the nucleotide.

heredity, blank s

blank r, D N A and R N A

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Figure 3.U N03

Figure 3.UN03 Testing your knowledge, question 10

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Figure 3.U N04

Figure 3.UN04 Testing your knowledge, question 12

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Figure 3.U N05

Figure 3.UN05 Testing your knowledge, question 15

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Figure 3.U N06

Figure 3.UN06 Testing your knowledge, question 18

Long Description:

On the horizontal axis temperature, temperature is shown in Celsius.. On the vertical axis, the rate of reaction is shown. Enzyme A has a hill leaning slightly to the right and has its peak at 38 degrees Celsius and its activity ranges from 0 degrees Celsius to 50 degrees Celsius. Enzyme B is also a hill leaning slightly to the right and has its peak at 78 degrees Celsius and its activity ranges from 40 degrees Celsius to 90 degrees Celsius.

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